The present invention relates to facsimile communication and, more particularly, to facsimile communication where image information is coded and transmitted so as to satisfy predetermined image quality.
Conventional facsimile communication, in particular, facsimile signal coding techniques, have pursued a subject as to how faithfully and fast an original picture can be transmitted.
On the other hand, facsimile communication has been diversified in recent years, and some of them do not always demand high resolution. That is, resolution is needed to be high enough only to recognize the contents of received image at the receiving side. For example, in case of transmitting very complex images or fine characters, high resolution is required if it is necessary to keep the quality of the received image high to a certain extent, but in case of transmitting simple images or large characters, high resolution is not always needed if it is necessary only to guarantee the same-grade image quality for the received images.
Heretofore, there have been established, from the abovesaid technical viewpoint, techniques by which the sender selects resolution in accordance with the property of the image to be transmitted. However, the prior art does not guarantee the image quality of the received image. Moreover, it does not fully satisfy the receiver's requirements and cannot be applied to the retrieval of the data base and so forth.
Further, facsimile communication has been effectively utilized for soft copy image communication as in the retrieval of an image data base as well as for conventional hard copy image communication. In the soft copy image communication, the method is useful, where a crude version of the image is transmitted and displayed quickly to recognize the contents of it as soon as possible, and the supplementary image information, if necessary, is added gradually to improve the image quality in order to reduce the transmission cost.